High-temperature components, such as gas turbine blades, are often cooled from the inside by means of a cooling medium, wherein this discharges from the turbine blades and contributes to film cooling.
In this case, it is essential for the function and the service life of the turbine blades that the passage is not blocked since otherwise local temperature increases and breaking off of the ceramic coating system can occur during operation.
These holes can be partially closed off during operation or during reconditioning if the cooling air holes are provided in the substrate and if a subsequent coating on the cooling air hole was not completely removed. There are a number of methods for checking passability, such as infrared camera and hot air excitation, or for checking the water passability and for visually determining whether water discharges from each cooling air hole. This, however, requires costly apparatus and needs time.
In particular, the application on the plant in remote places requires a quick quality check.